Include safe-ctype.h after C++ standard headers, to avoid over-poisoning

Include safe-ctype.h after C++ standard headers, to avoid over-poisoning

When building gcc's C++ sources against recent libc++, the poisoning of
the ctype macros due to including safe-ctype.h before including C++
standard headers such as <list>, <map>, etc, causes many compilation
errors, similar to:

  In file included from /home/dim/src/gcc/master/gcc/gensupport.cc:23:
  In file included from /home/dim/src/gcc/master/gcc/system.h:233:
  In file included from /usr/include/c++/v1/vector:321:
  In file included from
  /usr/include/c++/v1/__format/formatter_bool.h:20:
  In file included from
  /usr/include/c++/v1/__format/formatter_integral.h:32:
  In file included from /usr/include/c++/v1/locale:202:
  /usr/include/c++/v1/__locale:546:5: error: '__abi_tag__' attribute
  only applies to structs, variables, functions, and namespaces
    546 |     _LIBCPP_INLINE_VISIBILITY
        |     ^
  /usr/include/c++/v1/__config:813:37: note: expanded from macro
  '_LIBCPP_INLINE_VISIBILITY'
    813 | #  define _LIBCPP_INLINE_VISIBILITY _LIBCPP_HIDE_FROM_ABI
        |                                     ^
  /usr/include/c++/v1/__config:792:26: note: expanded from macro
  '_LIBCPP_HIDE_FROM_ABI'
    792 |
    __attribute__((__abi_tag__(_LIBCPP_TOSTRING(
  _LIBCPP_VERSIONED_IDENTIFIER))))
        |                          ^
  In file included from /home/dim/src/gcc/master/gcc/gensupport.cc:23:
  In file included from /home/dim/src/gcc/master/gcc/system.h:233:
  In file included from /usr/include/c++/v1/vector:321:
  In file included from
  /usr/include/c++/v1/__format/formatter_bool.h:20:
  In file included from
  /usr/include/c++/v1/__format/formatter_integral.h:32:
  In file included from /usr/include/c++/v1/locale:202:
  /usr/include/c++/v1/__locale:547:37: error: expected ';' at end of
  declaration list
    547 |     char_type toupper(char_type __c) const
        |                                     ^
  /usr/include/c++/v1/__locale:553:48: error: too many arguments
  provided to function-like macro invocation
    553 |     const char_type* toupper(char_type* __low, const
    char_type* __high) const
        |                                                ^
  /home/dim/src/gcc/master/gcc/../include/safe-ctype.h:146:9: note:
  macro 'toupper' defined here
    146 | #define toupper(c) do_not_use_toupper_with_safe_ctype
        |         ^

This is because libc++ uses different transitive includes than
libstdc++, and some of those transitive includes pull in various ctype
declarations (typically via <locale>).

There was already a special case for including <string> before
safe-ctype.h, so move the rest of the C++ standard header includes to
the same location, to fix the problem.

	PR middle-end/111632

gcc/ChangeLog:

	* system.h: Include safe-ctype.h after C++ standard headers.

Signed-off-by: Dimitry Andric <dimitry@andric.com>
(cherry picked from commit 9970b576b7e4ae337af1268395ff221348c4b34a)